Hydraulic radial piston machines



March 26, 1968 G. E. BJURKLUND 3,374,712

HYDRAULIC RADIAL PISTON MACHINES Filed April 25, 1966 3 sheets sheet l March 26, 1968 Filed April 25, 1966 c. E. 'BJORKLUND 3,374,712

HYDRAULIC RADIAL PISTON MACHINES 3 Sheets-Sheet INVENTOR. GUST/2F fe/kfiud'ekz o/va March 1968 G. E. BJORKLUND HYDRAULIC RADIAL PISTON MACHINES 3 Sheets-Sheet 5 Filed April 25, 1966 INVENTOR. 62/574; 56/? ddaEA Lu/VD United States Patent 3,374,712 HYDRAULIC RADIAL PISTON MACHINES Gustaf Erik Bjiirklund, Stockholm, Sweden, assignor to Rederi AB Soya, Hiigersten, Sweden Filed Apr. 25, 1966, Ser. No. 545,155 Claims priority, application Sweden, May 5, 1965, 5,886/ 65 Claims. (Cl. 91176) ABSTRACT OF THE DISCLOSURE A hydraulic radial piston machine comprises a central pintle serving as a valve for the working medium, a rotor mounted on the pintle, and pistons radially movable in cylinder spaces in the rotor. These spaces communicate with the pintle through ports, the rotor defining with the pintle an intake passage and a discharge passage, the cylinder spaces communicating with those passages through the ports. A track ring is mounted eccentrically of the pintle and rotor and surrounds the rotor and bears against the pistons to cause the pistons to reciprocate in the rotor upon rotation of the rotor. The pintle is provided with a holder mounted for movement in a direction to vary the eccentricity of the machine and for movement substantially at right angles to that direction. To do this, pistons are provided which are slidable in the holder, one of the pistons being urged away from the holder by the pressure of the high-pressure passage and the other of the pistons being urged away from the holder by the pressure of the low-pressure passage. In this way, differences in pressure in the intake and discharge passages are utilized to move the ring and the pintle relative to each other in an amount and in a direction such that the angle between the diametrical plane in which the ports begin to open into the intake and discharge passages and the diametrical plane in which the pistons reverse increases with increasing pressure difference.

Hydraulic radial piston machines of the type under consideration comprise a central pintle serving as a valve for the working medium, a rotor mounted on the pintle and having pistons radially movable in cylinder spaces each of which has a port which cooperates with the pintle and during rotation of the rotor on the pintle successively opens into and is shut off from an intake passage and a discharge passage in the pintle, and a track ring mounted in the casing of the machine eccentrically with respect to the pintle and surrounding the rotor. The ring bears against the pistons such that the pistons during rotation of the rotor reciprocate in the cylinders between outer and inner dead centers. Variation of the stroke volume in such a radial piston machine is usually effected by translational displacement of the rotor and the pintle with respect to the ring or in other words by variation of the eccentricity of the ring. During rotation of the rotor on the pintle the port of any cylinder will be closed on two occasions during each revolution, namely, when the port passes a cylindrical portion of the pintle between the inlet side and the outlet side thereof and also when the port passes another cylindrical portion on the opposite side of the pintle at the transition from the outlet side to the inlet side of the pintle. The cylindrical portions of the pintle which cooperate with the port of the working cylinder are circumferentially wider than the peripheral width of the port. From this it follows that during a certain angle of revolution the working medium in the cylinder will be entirely enclosed between the working piston in the cylinder and the cylindrical surface of the pintle. If in this position the piston moves inwardly from its outer dead center the working medium will be subjected to a certain compression. If, on the other hand, the piston is moving outwardly when the working medium is entirely enclosed between the piston and the pintle the working medium will expand to a certain degree. If now, irrespective of whether the working medium has been compressed or not or expanded or not, respectively, the pressure of the working medium at the very opening moment of the port is not equal to the pressure in the intake passage or discharge passage of the machine a pressure shock will arise as the port opens, resulting in pressure variations and annoying noises. The object of the present invention is to eliminate these inconveniences.

In its broadest aspect the invention is characterized in that the pintle together with the rotor in addition to the conventional possibility of displacement with respect to the ring for varying the eccentricity of the ring and consequently the stroke volume of the machine is further adjustable with respect to the ring in response to the difference between the pressures of the working medium in the intake passage and discharge passage such that the angle between the diametrical plane in which the ports begin to open into the intake and discharge of the pintle and the diametrical plane in which the pistons reverse increases with decreasing eccentricity and vice versa.

Additional characteristics of the invention will appear from the following description of an embodiment of the radial piston machine which is assumed to function as a pump. However, the invention is not limited thereto and can also be applied to hydraulic motors. In the drawings, FIGS. 1, 2, 3 and 4 are diagrammatic cross-sectional views of essential parts of a radial piston machine and explain the basic principle of the invention. FIGS. 5, 6 and 7 illustrate a constructional embodiment, FIG. 6 being a central longitudinal section, FIG. 5 across-section along the line 5-5 in FIG. 6, and- FIG. 7 a cross-section along the line 77 in FIG. 6.

Referring to the diagrammatic FIGS. 1 and 2, numeral 10 denotes the pintle of a radial piston pump having a rotor 12 and two diametrically opposite cylinders 14, 16 with pistons 18, 20 which are reciprocable in the cylinders by means of a surrounding track ring indicated by a circle 22. The common axis of the rotor and the pintle is indicated at 24 and the axis of the track ring is indi cated at 26. The pintle 10 has diametrically opposite recesses 28, 30, the recess 28 being in communication with the intake or low pressure side of the pump Whereas the recess 30 is in communication with the discharge or high pressure side of the pump. The chain-dotted line AA denotes the diametrical plane in which the pistons reverse and which hereinbelow is referred to as the eccentricity plane. If the liquid in the cylinders and the material of the surrounding parts of the machine were entirely rigid it would be suitable if the inner ends or ports of the cylinders would pass from the suction side to the pressure side or vice versa exactly in the eccentricity plane where the pistons have their dead centers. In practical constructions it is not possible, however, to obtain other than more or less elastic systems. The machine itself is slightly elastic, but above all the liquid has a certain compressibility. At an increase of pressure of about 2000 p.s.i. a hydraulic oil is compressed by approximately 1%. When the piston is in its outer dead center the oil has not yet been compressed in the cylinder. If the cylinder at that moment would be put into communictaion with the high pressure side where the pressure is f.i. 2000 p.s.i. oil

would return into the cylinder and energy would be lost.

Such loss may be considerable and increases in proportion to reduced length of stroke. The losses can be avoided however if the piston is permitted to compress the enclosed amount of oil to say 2000 p.s.i. before the cylinder is put into communication with the already compressed oil on the high pressure side, and if the enclosed high pressure oil which is to be put into communication with the low pressure side is permitted to expand down to the pressure prevailing on the low pressure side before the communication is opened. The compression and expansion under consideration can be obtained if the pe- 'ripheral surface 32 of the pintle which is passed by the than the port and if the pintle is turned through a certain angle a in the direction of rotation, as is shown in pressed in the cylinder 14 and expanded in the cylinder 16 to such a degree that the pressure in the cylinders at the high pressure passage and low pressure passage of the pintle, then no pressure shocks will arise. If the eccentricity of the track ring is changed from the greater value E shown in FIG. 1 to the smaller value E shown in FIG. 2 a greater angular deflection m of the pintle is required to obtain a certain piston movement at the desired compression.

Obviously, AS is equal for two opposite pistons only if the working volumes inwardly of the pistons are equal, i.e.,"if the eccentricity E is zero. In all other positions the compression AS and the expansion AS do not correspond to each other. However, if AS is chosen such as to be the'right one on the compression side for maximum eccentricity the expansion after a revolution of 180 will 7 port 34 of the cylinder is of greater peripheral extension 7 7 the opening moment is equal to the respective pressure in I be driven so far that a small void will be formed below 7 the piston, but this involves practically no loss. A maximum negative pressure of 14 p.s.i. during a piston movement of some tenths of a millimeter implies a very small loss of energy, but a noise occurs when the communication is opened and the void is filled. However, the volumes of the voids and the noises are very small.

, The range of travel during which the cylinder port is shut olf from the pintle cannot be made sufficiently great to obtain the described function in case of very short strokes. If said range of travel has a suitable mean value and due to the fact that the piston at great angular deflection a reverses its movement before the communication between the cylinders and the passages has been dis connected a compromise without practical inconvenience can be obtained.

1 To obtain the desired result, it is necessary to turn the pintle through an angle which is approximately proportional to the compression and consequently to the pressure on the high pressure side of the pump. The angular deflection of the pintle should also increase in a certain inverse proportionality to the length of the stroke. FIGS. 3 and 4 illustrate in principle how this is obtained FIG. 3 is a sectional view of the pintle 10 having recesses 28 and 30 on the low pressure side and high pressure side, respectively, and also shows part of the rotor 12.having two diametrically opposite inlet ports 34 to a pair of cylinders. The direction of rotation of the rotor is indicated at 36. With increasing pressure on the pressure side the pintle 10 should be turned in the direction of rotation. Instead thereof it is conceivable that the eccentricity plane AA is turned counter to the direction of rotation, as is illustrated in FIG. 4. The axis 26 of the track ring 22 is fixed whereas the common axis of the pintle and rotor is to be displaceable. FIG. 4 shows three' different positions B, B and B of said common axis.

rotor and pintle is moved from the position B to the p0 sition B with a resulting reduction of the eccentricity from E to E the eccentricity plane will be turned still more through an angle :2 from the initial position to the position A' A Both displacements of the axis B result in an increase of the angle on which is desirable because of the fact that it is possible thereby to obtain an increasing compression in the cylinder during the passage of the cylinder port past the wall of the pantle with decreasing eccentricity or length of stroke.

The embodiment shown in FIGS. 5 to 7 illustrates a practical application of the principles indicated above. In a casing 40 a holder 42 for the pintle 10 is displaceable for varying the strokes of the pistons 18, 20 disposed in a rotor 12 of a radial piston machinein which the track ring 22 is secured to a shaft 44 mounted in the casing 40. Displacement of the holder 42 is effected by 7 means of a lever 46 which is mounted on a pivot 48 in the casing of the machine and connected with the holder by an articulated rod 50. The pump has an intake passage 28 and a discharge passage 30. Provided on the high pressure side of the holder 42 is a radial cylinder .52

having a piston :54 the inner end of which is supported.

against a resilient member consisting of a pluralityof spring washers 56. On its outer. side the piston has a.

10 communicates through a duct 76 with the cylinder 52' on the high pressure side, and the high pressure passage 30 of the pintle communicates through a duct 78 with the cylinder 64 on the low'pressure side. 7

The magnitude of the force by which the working pistons 84, 86 on the high pressure side of the machine act upon the pintle in the direction a indicated in FIG. 7 depends upon the pressure of the working medium, the diameters of the working pistons and the number of the pistons. When the pressure in the machine rises the pintle 10 is moved slightly in a direction counter to the direction a, i.e., in the direction b in FIG. 7. Therefrom it will be seen that, in order to effect an adjustment in the direction b, the force exerted by the adjusting piston 66 must be greater than the opposite resultant of the forces exerted by the working pistons on the pintle.

If the holder 42 of the pintle upon an'increase of the pressure in the high pressure passage is moved in the direction b the spring washers 56 in the cylinder space 52' will be compressed while the spring washers in the cylinder space 64 at the piston 66 will relax. The spring great as is required to correspond to the desired change I of the angle a. The greater the diameter of the pistons 54 and 66 the stronger are the required spring washers.

It is obviously always possible to obtain sufliciently great displacing forces. The magnitude of the adjusting displacements will be understood from the fact that in a machine having a piston stroke of 16 mm. the displacement is approximately 1 mm. at a pressure of about 2800 p.s.i. gauge.

By means of the threaded adjusting plugs 60, 74 the spring washers 56, 68 can be precompressed so that the washers on both sides are compressed in the whole pressure range. The plugs also permit adjustment of the pintle in a position in which a=0 if the pressure is zero.

It should be noted that the desired adjustment of the angle a is obtained at any position of the holder 42 of the pintle, i.e., at any adjusted piston stroke, due to the fact that with a'certain lateral displacement of the pintle by means of the adjusting pistons 54, 66 the angle on automatically will be increased with decreasing eccentricity and vice versa.

I claim:

1. A hydraulic radial piston machine comprising a central pintle serving as a valve for the working medium, a rotor mounted on the pintle, pistons radially movable in cylinder spaces in the rotor, said spaces communicating with the pintle through ports, the rotor defining with the pintle an intake passage and a discharge passage, the cylinder spaces communicating with said passages through said ports, a track ring mounted eccentrically of the pintle and rotor and surrounding the rotor and bearing against the pistons to cause the pistons to reciprocate in the rotor upon rotation of the rotor; the improvement comprising a holder for the pintle, means mounting the holder for movement in a direction to vary the eccentricity of the machine, and means mounting the holder for movement substantially at right angles to said direction, said right-angle movement means comprising pistons slidable in the holder, one of the pistons being urged away from the holder by the pressure of the high-pressure passage and the other of the pistons being urged away from the holder by the pressure of the low-pressure passage, whereby difi'erences in pressure in the intake and discharge passages may be utilized to move the ring and the pintle relative to each other in an amount and in a direction such that the angle between the diamtrical plane in which the ports begin to open into the intake and discharge passages and the diametrical plane in which the pistons reverse increases with increasing pressure difference.

2. A machine as claimed in claim 1, the high pressure piston being bodily located on the low pressure side of the pintle and the low pressure piston being bodily located on the high pressure side of the pintle.

3. A machine as claimed in claim 1, and spring means yieldably urging the pistons radially outwardly.

4. A machine as claimed in claim 3, the machine having a stationary casing, and means acting between the casing and the pistons to precompress the spring means.

5. A machine as claimed in claim 1, the machine having a stationary casing, and thrust members disposed between the pistons and the casing.

References Cited UNITED STATES PATENTS 1,398,788 11/1921 Mayer 9l204 1,518,851 12/ 1924 Hutchinson et a1 9 1204 2,179,071 11/1939 Wiedmann 10338 3,051,092 8/1965 Lambeck 91-205 3,188,918 6/1965 B-jorklund 9l204 MARTIN P. SCHWADRON, Primary Examiner. PAUL E. MASLOUSKY, Examiner. 

